Changed the reply of BGSAVE and BGREWRITEAOF from +OK to a more meaningful...

Changed the reply of BGSAVE and BGREWRITEAOF from +OK to a more meaningful message that makes the user aware of an operation that just started and is not yet finished.

redis.c

@@ -3295,7 +3295,8 @@ static void bgsaveCommand(redisClient *c) {
         return;
     }
     if (rdbSaveBackground(server.dbfilename) == REDIS_OK) {
-        addReply(c,shared.ok);
+        char *status = "+Background saving started\r\n";
+        addReplySds(c,sdsnew(status));
     } else {
         addReply(c,shared.err);
     }
@@ -6082,7 +6083,8 @@ static void bgrewriteaofCommand(redisClient *c) {
         return;
     }
     if (rewriteAppendOnlyFileBackground() == REDIS_OK) {
-        addReply(c,shared.ok);
+        char *status = "+Background append only file rewriting started\r\n";
+        addReplySds(c,sdsnew(status));
     } else {
         addReply(c,shared.err);
     }

redis.conf

@@ -130,6 +130,9 @@ databases 16
 # log file at startup ignoring the dump.rdb file.
 #
 # The name of the append only file is "appendonly.log"
+#
+# IMPORTANT: Check the BGREWRITEAOF to check how to rewrite the append
+# log file in background when it gets too big.
 
 appendonly no